At exactly the moment Mark Carney's government was presenting what Ottawa described as "comprehensive proposals" to resolve its trade disputes with Washington, the White House announced a 50% tariff on most Canadian imports — a rate steep enough to reorder supply chains that have been woven together across the border for decades. The new duties, which take effect in 30 days, cover an unusually broad basket of goods: wine, hockey sticks, cement, and — most consequentially — products that had been shielded from import taxes under the United States-Mexico-Canada Agreement (USMCA). That carve-out matters because the USMCA was specifically designed to give businesses on both sides of the border the confidence to invest in cross-border manufacturing. Energy products, fish, critical minerals and potash are excluded, as are steel and aluminium, which are already subject to separate national-security tariffs.

President Trump signed three proclamations under Section 338 of the Tariff Act of 1930 — a provision that several Democratic legislators sought to repeal last year, precisely because they feared it could be deployed to destabilise trade relationships. The White House argues that Canada "discriminates" against American automobiles, alcohol and cheese relative to other trading partners. Critics note, however, that Canada's own 25% tariff on US vehicles — the retaliatory measure that Trump cites as evidence of discrimination — was itself a direct response to earlier American duties imposed under the rationale of curbing fentanyl smuggling, a charge Ottawa has consistently disputed.